The uses of polymeric materials, including diolefin polymers, continues to grow rapidly in such diverse areas as protective paint coverings, wire insulations, structural panels for automobiles, piping and lubricating oil viscosity index improvers. In many of these applications, the stability of the polymer is of paramount importance. Hydrogenation of diolefin polymers greatly improves the stability of these polymers against oxidative, thermal, and ultra violet degradation. Polymer hydrogenation processes have therefore been studied for many years as a method to prepare novel materials with excellent stability and other desirable properties. Early processes utilized heterogeneous catalysts which were known to be useful for hydrogenation of low molecular weight olefins and aromatics. These catalysts included catalysts such as nickel on kieselguhr. A fine catalyst powder was preferred and large amounts of catalysts were required to complete the hydrogenation in a reasonable amount of time. Such processes were only partially successful, since the reaction requires the diffusion of the polymer molecules into the pores of the catalyst, where the active nickel metal was present. This is a slow process when hydrogenating polymers.
Discovery of nickel octoate/triethyl aluminum hydrogenation catalyst systems enabled rapid hydrogenation of polymers. These processes utilize the catalyst as a colloidal suspension in polymer containing solutions. This type of catalyst is referred to as a homogeneous catalyst. Such a process has been used for a number of years to prepare hydrogenated butadiene-styrene polymers. U.S. Pat. No. 3,554,991 describes an exemplary process. Besides nickel, Group VIII metals in general will function as the active metal in these systems, and in particular, iron, cobalt, and palladium are known to be acceptable.
Pore diffusion is not a limitation with homogeneous catalysts and the hydrogenation process is rapid and complete in a matter of minutes. However, removal of the catalyst from the polymer product is necessary because metals, and particularly nickel, which remain with the polymer catalyze degradation of the polymer product. The removal of the catalyst from polymer solutions is commonly accomplished by the addition of an ammonium phosphate-water solution and air and then filtration of solids which contain the catalyst particals from the polymer solution. The air is utilized to oxidize the nickel to a divalent state.
Alternative methods to remove hydrogenation catalyst residues from cements of hydrogenated polymers include treatment with an amine compound wherein the amine is either a chloride salt or a diamine having an alkyl group of 1 to 12 carbon atoms as disclosed by U.S. Pat. No. 4,098,991; and treatment with a non-aqueous acid followed by neutralization with an anhydrous base and filtration, as disclosed by U.S. Pat. No. 4,028,485.
Some of these catalyst removal systems are undesirable because those processes require relatively expensive metallurgy due to the corrosive nature of the nickel removal compounds. Many also produce an aqueous acidic sludge containing the catalyst and residues of the treatment chemicals. It can be difficult and expensive to dispose of this sludge.
Treatment of polymer cements to remove hydrogenation catalyst residues can also be accomplished by contacting the cement with dicarboxylic acid and an oxidant, as disclosed in U.S. Pat. No. 4,595,749. In this process, the dicarboxylic acid is first dissolved in toluene, ethanol, or another solvent for the polymer. This method is advantageous because it can be accomplished in equipment fabricated from inexpensive materials. This process also does not produce an acidic aqueous stream which requires disposal because the catalyst residue metals and acid precipitate directly from the polymer cement. However, it has been found that this process has the disadvantage of requiring an excessive amount of time for the precipitate to form.
It is therefore an object of this invention to provide a process to remove Group VIII metal containing hydrogenation catalyst residue from polymer cements. It is a further object of this invention to provide a process to remove hydrogenation catalyst residue from polymer cements which does not produce an aqueous phase of reactants. It is another object to provide a process where hydrogenation catalyst residue can be removed from polymer cements by precipitation of the residues wherein the precipitation is rapid and results in solid particles which are easily removed from the polymer cements. It is another object of this invention to provide a process which is capable of removing hydrogenation catalyst residues from polymer cements to a level of 10 ppm of Group VIII metals or less based on the polymer.